Valve rotating devices of such kind are known for instance from DE-AS 1 293 789, U.S. Pat. No. 2,827,886, DE-OS 2 757 455 or from DE-OS 30 04 320. These valve rotating devices are employed in internal combustion engines, in particular in large diesel engines, in which the valve seat and the valve stem are exposed to a relatively high degree of wear. A valve rotating device serves to achieve a uniform thermal loading and therefore wear of the valve and in addition to this makes a decarbonization of the valve seat.
In conventional valve rotating devices the cover is rotatably supported by a disk-shaped cup spring, which rests directly on the balls of the basic body. The balls are arranged in ball pockets with inclined ball races in the basic body whilst being distributed in the circumferential direction, and in doing so the balls are retained by means of tangential springs at an upper point of the inclined ball races. When the valve is opened the cup spring presses on the balls, whereby these roll to the lowest point of the inclined ball races in the basic body. In doing so the cup spring rotates. The tangential springs are compressed. The rotary movement of the cup spring is transmitted via the cover, the valve spring, the upper spring disk and by means of clamping parts to the valve. When the valve closes the cup spring is relieved. The balls are moved back into the initial position again by the tangential springs without rolling. As a result, a rotation only takes place during the opening of the valve, whereas during the closing there is no retrograde rotation. In the case of an upward disposed valve rotating device the basic body can also support itself through a valve spring on the engine block.
It is true that a good rotation is attained with these known valve rotating devices. However, the service life of these known valve rotating devices is limited, as a considerable wear, referred to as pitting formation, is caused on the rotating device both on the balls and on the ball races in the ball pockets.
In the valve rotating device according to WO 01/73270 an appreciable reduction of wear and consequently a corresponding increase in service life is achieved. However, even in the case of this improved valve rotating device the actual rotary movement is brought about by ball races inclined in the axial direction and balls that are being pressed into the ball pockets as a result of the axial valve force.
From U.S. Pat. Nos. 1,414,499 and 1,479,169 rotating devices are known, in which the rotary movement is generated in the manner of a mechanical cam control. A pin is guided in a helical groove of a bushing. In order to transmit the rotary movement in one stroke direction only, an axial coupling having two geared rings lying opposite each other is provided. Here a part of the stroke movement of the valve stem is required as a coupling movement for the coupling and uncoupling and is not available for the rotary movement.